The objectives of this research program are a detailed analysis of the role of chemical carcinogens on the induction of preneoplastic mammary lesions and their transformation into neoplasms. Both alveolar and ductal hyperplasias are being characterized, with respect to their morphological characteristics, their tumor potential, their hormone dependency in vivo, and their immunogenic characteristics in vivo and in vitro. In addition, experiments have investigated the immunosuppressive effects of chemical carcinogens and its significance in the neoplastic transformation as it occurs in the mammary gland. Experiments also have documented the effects of chemical carcinogens on pituitary prolactin concentration and will investigate plasma pituitary levels.